Phase-Plane Approximations in the Analysis of an Undamped Nonlinear Circuit

Approximate solutions to ϕ+f(ϕ)=0 are developed by truncating f(ϕ) to a cubic and solving for the unknown coefficients by matching in the phase-plane. The object of the development is to show that the phase-plane represents a useful set of parameters with which one can develop flexible approximate solutions.